The present invention relates to the field of memory programmable controllers of the type having cyclically traversed user control programs which operate on process images stored in a data memory of the controller. The process images once the control program has executed a full cycle, are used to control a peripheral process. In particular, the present invention relates to memory-programmable controllers of the multiprocessor type including a word processor which processes operating system and word commands, a bit processor which processes binary interlinking commands, a user program memory in which the control program is stored, an operating system memory in which an operating system program is stored and a data memory wherein the binary process images of the peripheral process under control are stored.
Memory-programmable controllers are described in detail, for instance, in Siemens Zeitschrift Energietechnik 1979, no. 2, pages 43 to 47, in no. 4, pages 136 to 139, in European Patent No. 10170 and in U.S. Pat. Nos. 3,921,146 and 3,942,158.
Presently popular microprocessors, called word processors in the following because they process data in parallel groupings called words, are as a rule designed, as far as their command sets are concerned, for a broad group of users, i.e., universally. In the course of development, the size and performance of the command sets are increasing steadily. It is also characteristic of this development that more and more information carriers (bits) are combined and processed in parallel, i.e., in word groups, e.g. 8 bits in a word.
There are, however, special applications in which largely information one bit wide must be processed. One bit, for instance, independently of others, may carry information on peripheral process conditions, such as whether a switch is "on" or "off", or whether controlled process input conditions are met or not met.
A memory-programmable controller of the type mentioned above should preferably be able to carry out bit operations, i.e., logical interlinking of data one bit wide, as well as more complex functions with data one word wide, such as arithmetic functions, data transfer, timing etc.
It is therefore advantageous to use within the scope of a memory-programmable controller a multiprocessor system, in which the execution of one bit binary commands is assigned to a separate fast bit processor, while a relatively slow word processor carries out the more complex functions involving words (see, for instance, Siemens-Zeitschrift Energietechnik 1980, no. 9, page 361).
Since the word-wide and bit-wide processing of the data is mixed and in part independent of the other, a special arrangement for coupling and synchronizing the processors is required. It must also be taken into consideration that the word processor must additionally execute special routines at definite intervals as well as operate completely asynchronously to the program cycle proper, e.g., word and bit operations. Additionally, the program cycle proper with bit- and word-wise data processing should be loaded as little as possible by these routines, but should have the lowest priority, i.e., as soon as the processing of one of these special routines is required, the latter must be performed immediately and unconditionally.